The present invention relates to the handling of wafers, and more particularly to handling and testing semiconductor wafers in a wafer testing apparatus.
The manufacture of integrated circuit (IC) chips begins with blank, unpatternd semiconductor wafers. These wafers undergo a number of sometimes critical process steps before being formed into the final IC chip form. A substandard wafer can affect the yield (i.e., number) of usable IC chips on a wafer. It is therefore desirable to have a machine for testing wafers to ensure that the wafers meet a desired standard to maximize wafer yield.
Testing of the wafers typically involves an automated process utilizing automated wafer handling machines. In this process, the automated wafer handling machines continuously handle and test the wafers. The automated process tends to be more efficient than manual testing and handling of wafers since an automated process is typically faster, more precise, and less prone to contamination than a manual process.
One of the major uses of the automated wafer handling machines is for testing or processing the wafers to determine or change certain wafer characteristics (such as by depositing a film or removing a wafer layer). For example, automated wafer handling machines are often used to determine the orientation of a wafer, which provides a standard reference against which the location and characteristics of test points on the wafer may be measured.
A conventional art wafer handling machine has a four degree of freedom. In this machine, the wafer cassette moves up and down, the chuck rotates, the arm moves from left to right. However, one of the drawbacks of the conventional wafer handling machines is movement of the wafers within the wafer cassette. For example, when the wafer cassette moves up and down to allow a robot arm to remove a wafer from the cassette or place a wafer into the cassette, the wafers within the cassette may be subject to unwanted jarring. The vibrations caused by the jarring are potentially harmful due to the creation of particle contaminants.
In addition, the conventional wafer handling machines typically include a motor for each degree of freedom for a total of four motors. Generally, moving parts in a machine or apparatus such as motors are more prone to failure and require more maintenance than non-moving parts. Further the use of such number of motors typically require complex and costly mechanisms that require more maintenance, which is undesirable in production environments.
Thus, what is needed is an apparatus and method that can efficiently move and test wafers without moving the wafer carrier or cassette. In addition, what is needed is an apparatus and method that can move and test wafers using less number of motors so as to reduce the cost and maintenance involved with the motors.